Sagittal Plane Lifting Research Articles

Regression models for the prediction of dynamic L4/L5 compression forces during lifting

The purpose of this study was to determine whether regression equations could be developed, as an alternative to biochemical models, to predict the peak L4(L5 disc compression force during dynamic, sagittal plane lifting. Eighteen male subjects performed a squat and a stoop lift with loads of 6, 14, 22, 29, and 32 kg. Each lift was analysed with a linked segment biomechanical model that output the compression force time history during the lift. The peak compression served as the dependent variable for two regression models. The independent variables in each model were measures which described the subject's body dimensions, body posture, internal lifting mechanics, load location and load effects. A ‘lab’ model was developed (R2=0·93) which required only four inputs and had an RMS error of only 8·3% between the biomechanical model estimate of the peak L4/L5 disc compression force and that predicted from the regression equation. A seven variable ‘field’ model was developed with an R2 of 0·90 and an RMS error of 9·7%. It was concluded that both of the proposed models were potentially useful to the practising ergonomist interested in easily and quickly estimating lumbar compression forces during dynamic sagittal plane lifting.

Lifting low-lying loads in the sagittal plane.

A simple geometrical model was employed to investigate various elementary techniques during static, sagittal plane lifts. Relationships between the various joint reaction forces were deduced. In particular, it was found that it is possible to simultaneously increase (or decrease) both knee and low back forces. In terms of the total force on the low back, hip, knee, and ankle joints, vertical back lifting is generally not recommended. This is especially true when lifting low-lying objects from the ground. However, minimization of loads is not the only factor to consider when analysing the optimal technique of a certain lifting task. Several other cost functions have been previously proposed. Comparisons derived from minimizing various cost functions suggest that the minimization of the maximum necessary muscle intensity may be the most appropriate in deducing optimal load lifting configurations.

Accuracy of a ratio-estimation method to set maximum acceptable weights in complex lifting tasks

This study evaluated the accuracy with which trained and conditioned females could set Maximum Acceptable Weights (MAWs) for different lifting tasks. Two types of lifting tasks were studied: a sagittal plane lifting task performed with four lift frequencies and two lift ranges, and a lift and twist task performed with four different lift frequencies. For the sagittal plane task the two lifting ranges were floor-to-knuckle and knuckle-to-shoulder, with lift frequencies of one lift every 9, 20, 60, and 120-seconds. For the lift and twist task the lifting range was floor-to-knuckle, the twist was 90 deg, and the lift frequencies were 20-seconds and 60-seconds. In each of the lifting tasks subjects set the MAW using the psychophysical method. Immediately after the MAW had been set, the task conditions were changed, the task was performed for a few cycles with the original MAW, and rated using ratio-estimation. This rating was used to estimate a MAW for the second lifting task. On a later day, the MAW was set for the second task using the psychophysical method, and the MAW for the original task estimated with ratio-estimation. This allowed comparison of the accuracy of MAWs set by the psychophysical method and ratio-estimation. Consistent with previous research there were significant effects on the MAW due to frequency of lift, the lift range, and twisting. There were no significant differences between MAWs set by' ratio-estimation and the psychophysical method ( p > 0.6). This indicated that, (1) ratio-estimation is an accurate method to quickly establish MAWs for a lifting tasks, and (2) that MAWs for lifting tasks not easily determined may be quickly and accurately determined using ratio-estimation.

A biomechanical perspective of sacro-iliac pain

Pain in the sacroiliac region is often referred to by the non-specific term sacro-iliac syndrome. Quite often there is dull pain accompanied with local tenderness over the sacrum and posterior superior iliac spines. The hypothesis of this work is that the pain may result from surprisingly large stresses within the extensor aponeurosis and other extensor forces directly transmitted to the sacro-iliac region. The forces in 48 muscles were estimated from a detailed, anatomic computer model of the trunk. Forces in muscles that originate from the sacral and posterior superior iliac spine region were summated. For sagittal plane lifts involving relatively light loads of 27·3 kg, nearly 7 kN of force was transmitted to the extensor origins of the sacro-iliac region. A large proportion of this force was produced by the longissimus thoracis pars lumborum and iliocostalis lumborum pars lumborum complex. These predicted high stresses are discussed as possible factors in clinically observed sacroiliac trauma and pain.

The relationship between trunk muscle electromyography and lifting moments in the sagittal and frontal planes

In this study, we explore the relationship between moments in the frontal and sagittal planes, generated by a lifting task, vs the electromyographic (EMG) activity of right and left trunk muscle groups. In particular, we postulate that the functional dependence between erector spinae muscle activity and the applied lifting moments about the spine is as follows: (1) the sum of left and right erector spinae processed EMG depends on the sagittal plane moment, and (2) the difference of left and right erector spinae processed EMG depends on the frontal plane moment. A simple out-of-sagittal plane physical model, treating the lumbar spine as a two degree-of-freedom pivot point is discussed to justify these hypotheses. To validate this model, we collected surface EMG and lifting moment data for ten males performing a grid of frontal and sagittal plane lifting tasks. A digital RMS-to-DC algorithm was developed for processing raw EMG. For these tests, we measured EMG for the left and right erector spinae and for the left and right external oblique muscles. The processed EMG signals of the left and right erector spinae muscles are summed and differenced for comparison to the measured sagittal and frontal plane moments. A linear correlation ( r 2) of 0.96 was obtained for the sum of erector spinae EMG vs the sagittal plane moment; a corresponding value of r 2 = 0.95 was obtained for the difference vs the frontal plane moment. No correlations ( r 2 < 0.004) was found for (1) the sagittal plane moment and the difference of the left and right erector spinae EMG, and (2) the frontal plane moment and the sum of the left and right erector spinae EMG.

Partitioning of the L4-L5 dynamic moment into disc, ligamentous, and muscular components during lifting.

This work describes a dynamic model of the low back that incorporates extensive anatomical detail of a three-dimensional musculo-ligamentous-skeletal system. The reactive moment about L4-L5, determined from sagittal plane lifts, was partitioned into restorative components provided by the disc in bending, ligament strain, and active muscle contraction. Skeletal kinematics were obtained from cine analysis of markers on the rib cage and pelvis. The musculature was driven from surface EMG collected from six sites. When compared with past models, features of this model included improved anatomical modeling, improved monitoring of vertebral motion unit kinematics, improved estimation of neural activation of the musculature, and consideration of the effects of muscle length, velocity, cross-sectional area and passive elasticity in force estimation. Estimations of L4-L5 disc compression and shear were, on average, 16.2% and 42.5% lower, respectively, than those calculated from a simple 5 cm erector tissue moment arm length. There was no need to invoke intra-abdominal pressure or other contentious compression-reducing mechanisms. Muscle activity, particularly that of the sacrospinalis, dominated the generation of the restorative moment. Ligaments played a very minor role in the lifts studied. High muscle loads are consistent with the common clinical observation of muscle strain often produced by load handling.

Model for static lifting: Relationship of loads on the spine and the knee

An experimental study based on a trigonometric, anthropometric model, was conducted on thirty-five healthy subjects to determine the relationship between knee and back forces during symmetric sagittal plane lifting. Total joint reaction forces for the knee and the back, along with their compressive and shear components, were calculated for each subject, as a function of the knee, back and ankle angles. The shear component was significantly higher in females than in males; the compressive component was significantly higher in males. Strong inverse correlations were found between the back and the knee forces on all subjects. Strong correlations were also found between subject anthropometry and minimum and maximum joint reaction forces. The magnitudes of both back and knee joint reaction forces should be considered in recommending the lift type and position, based upon individual worker anthropometry, and size and weight of the load to be lifted.

A Biomechanical Model for Analysis of Symmetric Sagittal Plane Lifting

Abstract A computerized model of the human body is developed. It assumes the skeletal muscle system to be analogous to a series of eight solid links representing the major body segments which are articulated in a manner corresponding with selected body joints. It is shown by empirical tests that the model can be used to predict the maximum strengths of persons asked to lift objects while assuming different postures. It is proposed that this type of model represents a rational method for investigating the many variables that affect the physical strength capability of any individual required to perform materials-handling activities.